1. EXPERIENCE WITH LI-6400 PORTABLE PHOTOSYNTHESIS SYSTEM
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EXPERIENCE WITH LI-6400 PORTABLE PHOTOSYNTHESIS SYSTEM
S.M. Sitompul
Lab. Plant Physiology, Faculty of Agriculture, University of Brawijaya
4/14/2019

2. PRESENTATION OUTLINE
1. INTRODUCTION 1. Importance of Photosynthesis 2. Green Revolution 3. C4 Rice Project 2. CASE STUDY OF SOYBEAN 1. Soybean Productivity 2. Soybean Photosynthesis 3. LICOR-6400 and CER
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3. INTRODUCTION 1. Importance of Photosynthesis
Photosynthesis is central to all life on earth, providing O2 and organic compounds that are synthesized from atmospheric CO2 and water using radiation energy.
Photosynthetic organisms convert more than 109 tons of atmospheric CO2 into biomass per year.
A serious challenge faced with the still-increasing world population from ~7 billion now to 9–10 billion by 2050, is to further enhance biomass production of crop plants.
The production of biomass is determined at first by the available solar irradiation energy intercepted by crops across the growing season (0.487 Si).
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4. Other factors are the conversion efficiency of intercepted radiation into crop biomass (εc), and the fraction of the total biomass partitioned into the harvestable part of the plant [harvest index (HI), εp].
Monteith integrated the factors determining crop yields into an equation as follows:
2. Green Revolution
The Green Revolution raised the yield potential of the major grain crops mainly by increasing the HI, which is now about 0.6.
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5. Breeders were also able to improve the light interception efficiency, which in modern cultivars is up to about 0.8–0.9.
All available evidence suggests that additional grain yields by further increasing the HI or optimizing light interception are rather unlikely which appear close to biological limits.
In a recent review (Flügge et al., 2016), the best light conversion efficiency (εc) observed in field experiments (0.24 in C3- and 0.37 in C4-crops) is far below the theoretical maxima (0.46 in C3- and 0.6 in C4-plants).
Therefore, a prime target in order to increasing crop yield is to increase the rate of crop photosynthesis through;
increasing light distribution within and light interception by crop canopies.
light reaction efficiency (light harvesting process including regulators of photosynthetic electron flow).
Increasing efficiency of CO2 reduction.
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6. The most promising targets for genetic engineering of the light reactions of photosynthesis––in terms of manipulating one or a few genes––are modifying light harvesting and regulators of photosynthetic electron flow (Flügge et al., 2016).
The measurement of CO2 exchange rate (CER), or apparent photosynthesis, is thus of great importance.
3. C4 Rice Project
The only way to achieve the rice harvests needed for the future is considered to change the biophysical structure of the rice plant, making it a much more efficient user of energy from the sun.
Rice has a C3 photosynthetic pathway, less efficient than that of maize, which has a C4 pathway.
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7. C3 plants
RUBISCO
Calvin cycle
C4 plants

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9. C4 Photosynthesis: PEP Carboxylase then Rubisco
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10. Figure 1 Anatomical differences between C3 and C4 leaves
Figure 1 Anatomical differences between C3 and C4 leaves. (A) C3 (Oryza sativa L., rice variety IR64) and (B) C4 (Setaria viridis) leaf.
Mesophyll cell (MC) of rice is filled with chloroplasts which is more than 90% of the total chloroplasts, whereas, the bundle sheath cells (BSC) have very few number of chloroplasts which account for less than 10% of the total chloroplasts in the rice leaves. In C4 leaf, chloroplasts are localized in BSC as well as in MC. Source: Karki et al. (2013)
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12. CAM plants
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13. 2. CASE STUDY OF SOYBEAN 1. Soybean Productivity
The production of soybean in Indonesia is far below the rate of consumption, and the production deficit is met by import.
As an illustration in 2015;
The rate of consumption was kg cap-1week-1 ( kg cap-1 year-1).
An estimated population was 255,461,700.
The total consumption of soybean would be 3,692,954 tons.
The total production of soybean was 963,183 tons
It was more than 70% of soybean supply to be met by import in 2015.
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14. 2. Soybean Photosynthesis
Soybean production is the product of harvested area (ha) and productivity (ton ha-1).
Productivity or yield is the product of the following parameters:
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15. Therefore, the yield of soybean is about SOURCE AND SINK.
The yield of soybean is considered to
be more limited by sink than source
strength.
In general, source strength is the main
factor limiting the yield of C3 plants.
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16. 3. LICOR-6400 and CER
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17. Table. Readings with LICOR-6400 converted to an excel format
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18. PAR PHS (mol CO2 m-2s-1) Trmmol (mmol H2O m-2s-1) Ci (mol CO2 mol-1)
Table. An example of results measured with LICOR-6400
PAR
PHS (mol CO2 m-2s-1)
Trmmol (mmol H2O m-2s-1)
Ci (mol CO2 mol-1)
1501
14.7
3.31
245
1001
14.8
2.98
233
501
11.9
2.68
253
300
10.9
2.27
244
200
7.98
2.08
273
100
5.22
1.5
282 49
3.67
1.48
314 19
1.29
1.32
359
0.106
1.17
386
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19. F2 soybean plants (reciprocal crosses between var. Brawijaya x var
F2 soybean plants (reciprocal crosses between var. Brawijaya x var. Argomulyo.
Genotypes
(F2)
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20. QE = quantum efficiency = mol CO2/quantum
Analysis
QE = quantum efficiency = mol CO2/quantum
I = irradiance (mol quanta m-2s-1)
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21. SOLUTION Linearization approach P/Pmax = [1-EXP(QE.I/Pmax)]
ln(1-P/Pmax) = QE/Pmax*Iy = ax + b
y = ln(1-P/Pmax)
x = I (irradiance)
a = QE/Pmax, and
b = 0
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23. In 30 F1 plants (reciprocal crosses), Pod Number was not closely related to CER (apparent photosynthesis)
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24. As expected, Seed Number was not closely related to CER (apparent photosynthesis).
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25. Seed Weight (g/100 seeds) was also not related to CER (apparent photosynthesis).
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26. Total Seed Weight (g/plant) was also not related to CER (apparent photosynthesis).
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27. However, Total Seed Weight (g/plant) was closely related to Seed Number per plant.
It is hypothesized that total photosynthesis per plant or per area is more important than the rate of photosynthesis pe unit leaf area as a determinant of seed yield.
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28.
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29. Figure 3 Simplified biochemical pathway of NADP-ME subtype of C4 photosynthesis that is being genetically engineered into indica rice variety by the C4 rice consortium. Source: Karki et al. (2013) 
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